Resinous composition for coating electric conductors

ABSTRACT

A magnet wire characterized by an insulating resinous coating composition used as base coat and/or topcoat over a different base coating, said coatings having a low coefficient of friction. These coatings retain the ability to be overcoated with other coatings such as wire varnishes and enamel. The coatings, such as the reaction product of a polytrimellitamideimide film-forming resin and methyl tetradecyl polysiloxane, are applied in single or multiple coats from solutions over the wire or a base-coated wire, each coat being cured in an oven to cause the polymers to react or interact to produce smooth, hard, slippery surfaces.

United States Patent Jerome A. Preston Fort Wayne, Ind.

[21] Appl. No. 790,887

[22] Filed Jan. 13, 1969 [45] Patented Jan. 4, 1972 [7 3] Assignee Essex International, Inc.

[72] Inventor [54] RESINOUS COMPOSITION FOR COATING 3,044,980 7/1962 Modic et a1. 260/824 3,170,890 2/1965 Boyd et a1 260/824 EP 3,305,504 2/1967 Huntington 260/824 3,358,064 12/ 1967 Belko i 260/824 EP 3,379,790 4/1968 Krauss et a1. 260/824 3,423,479 1/1969 Hendricks 260/ 824 3,440,203 4/1969 Boldebuck et a1. 260/824 3,449,465 6/1969 Golitz et a]. 260/ 824 3,462,513 8/1969 Fitzhugh 260/826 3,475,512 10/1969 Baugh et a1. 260/824 Primary Examiner-William D. Martin Assistant Examiner-Raymond M. Speer Attorney-Molinare, Allegretti, Newitt & Witcoff ABSTRACT: A magnet wire characterized by an insulating resinous coating composition used as base coat and/0r topcoat over a different base coating, said coatings having a low coefficient of friction. These coatings retain the ability to be overcoated with other coatings such as wire varnishes and enamel. The coatings, such as the reaction product of a polytrimellitamideimide film-forming resin and methyl tetradecyl polysiloxane, are applied in single or multiple coats from solutions over the wire or a base-coated wire, each coat being cured in an oven to cause the polymers to react or interact to produce smooth, hard, slippery surfaces.

RESINOUS COMPOSITION FOR COATING ELECTRIC CONDUCTORS This invention relates to an improved magnet wire having a resinous insulating coating characterized by a low coefficient of friction, and to the method of making the coating.

It is an object of the present invention to provide magnet wire which requires no oil for winding, that is, the coefficient of friction of the coating is so low that it can be wound at high speeds without pretreatment of any kind. The wire of this invention has a slippery, dry surface which makes high-speed winding possible, but the slick nature of the surface does not prevent overcoating or adhesion of other coatings. The coating provides a significantly superior dry lubricity with an oilfree surface, resulting in significant advantages: cleaner winding and therefore cleaner shop and material storage areas because dust and dirt will not collect as readily as where ordinary mineral oils are used; no oil can be thrown from the wire or burned due to heat developed from friction; reduction in contamination of wound units with foreign material, improving product reliability; obviating problems resulting from inconsistent lubrication due to the excess or lack of oil application; and improved space and wire utilization results from winding units with reduced mean turn lengths because the slippery wire coils slide into tight, closely-abutting relation during winding to eliminate unnecessary spaces therebetween.

The wire of the invention also allows winding machines to operate at the maximum winding speeds; therefore, better efficiencies are obtained. More compact windings allow improvement in balance of rotating parts and reduced loading of bearings and bushings. Additional insulations such as slot wedges can be more easily placed in units because of the improved space factors.

Work hardening of metal conductors is a problem in wind ing magnet wire, and wire made in accordance with my invention reduces this problem because high-winding tensions are not needed. Forming operations are facilitated and forming procedures on conductors are equalized because the wires slide past one another when formed. Coil windings made from wire coated according to this invention require less effort to seat and insert by various winding and forming devices.

Taping of coils wound with wire made from this invention is more readily accomplished, tapes will stick to the wire and no oil removal procedures are necessitated. Better varnish coverage, spray and/or dipping techniques, are accomplished since no oil is present to interfere with the wetability of the varnish or other coatings. Many current encapsulants of wound units are plagued by entrapped air and/or oil left on wire by conventional wire operations. Encapsulation, thus, is improved because no trapped oil is present in units made from this invention.

Nylon insulations have long been recognized by the magnet wire industry as the most windable films available, due to their slick surfaces and consequent ability to nest into allotted winding spaces. The new resin coatings of my invention consistently outperform the nylon types based on comparative tests on high-speed automatic winding equipment and in laboratory-controlled coefficient of friction tests.

Wire coatings of the invention exhibit a percent coefficient of friction improvement over nylon and up to 90 percent over other common films. In these tests, optimum windability is predicted by the lowest coefficient of friction value. The coefficient of friction obtained on any insulation is primarily due to the material used for the outer coating and can be affected to a limited degree through the use of spooling oils or other topical lubricants. For nylon over-coated insulations, the coefficient of friction is 0.17; with other commonly used films it ranges up to 0.33. For insulation of the invention, it consistently measures 0.14 or below.

Most products produced from magnet wire must be further coated with bonding varnish, or where no varnish, enamel or paint is used to over coat a magnet wire, electrical tapes of various types may be needed to hold the magnet wire shapes in position. These tapes likewise must adhere to these slippery coatings. The resin coatings of the invention possess tape and varnish adhesiveness which is responsible in large part for the success of the invention.

The foregoing objects and advantages of my invention may be accomplished by coating wire with a conventional coating resin, e.g. polyamides, polyester, polytrimellitamide-imide, alkyd, epoxy and the like, modified by the addition of from 0.0l to 25.0 percent by weight of a two-dimensional linear organo polysiloxane based upon the weight of the resin. The polysiloxane may have the following formula:

Where R is an alkyl or aryl radical, R is an alkyl radical or unsaturated organic material or side chain having from one to 20 carbon atoms or more, R, is an alkyl radical and/0r H, OH, and COOH or unsaturated side chain, and n equals 2- l 0 or more.

The operable polysiloxanes have a molecular weight ranging from 600-8,000, with 2,500 as a median, and a viscosity of from l200,000 centistokes at 77 F. with a median of 1,500. These compounds are known to the art and may be prepared by the hydrolysis of di-organo di-halogen silanes, such as methyl phenyl di-chlorosilane or' methyl ethyl di-chlorosilane, followed by the partial condensation of the hydrolysis product and further reacted or copolymerized with an unsaturated organic material.

The nature of the polysiloxane polymers is critical inthe practice of the invention. Polymers such as dimethyl polysiloxane of various molecular weights provide a surface having a low coefficient of friction when incorporated with various resins. However, most paints, enamels, varnishes and tapes will not adhere to such a surface. On the other hand, monomeric silicones or three-dimensional resinous silicones have varnish adhesiveness, but are not suitable since they do not impart the desired'slipperiness. It is necessary to use linear dimethyl polysiloxane polymers having a pendant radical-attached to a silicon atom directly or through CH groups, or as an end group, that will accept a bondiwith aresinous coating. The silicone polymers mayhave a variety of organic side groups along the basic polymer chain (Si-OSi). These may, be methyl, ethyl, propyl, butyl, phenyl, carboxyalkyl, methyl alkyl, hydroxyalkyl, cyanoalkyl, or aminoalkyl. Of these, methyls and phenylsare used most extensively.

The coatings of the invention are prepared by mixing the aforesaid polysiloxanes with a'solution of certain film-forming resins and/or elastomers commonly used as wire coatings, preferably in a quantity from 0.l0 to 5 percent based on the weight of the resin. The polysiloxane polymers interact and react at elevated temperatures to combine with the conventional coating resin to form a hard, dry, slippery surface. Among the conventional coating resins which may be modified in accordance with the invention are polyesters, polyamides, polytrimellitamide-imide, polyvinyl butyral, polyvinyl formal, polyvinyl formal-phenolic, polyvinyl formalisocyanate, polyurethane, epoxy, acrylic, alkyd, polycarbonate, polypropylene, polyhydantoin, and compatible mixtures thereof.

The probable mechanism by which the polysiloxane is cured is by oxidation. This may be triggered by heat when an oxidation threshold is reached and free radicals are formed. A catalyst may or may not be used to help trigger this reaction. ln oxidation breakdown, oxygen reacts with the organic groups of the molecules gradually increasing the viscosity of the polysiloxanes until gelation occurs. The reaction is dependent upon temperature and. the supply of oxygen present. Some of the operable polysiloxane polymers have pendant or terminal hydroxy groups in low quantity that can be activated at room temperature by means of a catalyst or at elevated temperature. These may tend to keep the silicones in stable solution or dispersion with the resin components being modified.

When the wire is passed through a resin-polysiloxane coating solution and then through a vertical tower or other suitable oven maintained at a temperature of from 200500 C., the desired coating is formed. The silicone in the cured coating does not bleed to the surface and is effective in reducing the coetficient of friction of from 20-50 percent compared with the same coating from which the polysiloxane has been omitted, depending upon the particular resin solution to which it is added. Additionally, the presence of the polysiloxane may improve the resistance of the coating to ozone, moisture, and heat.

Several types of polysiloxanes are useful as modifiers in this invention One is a dimethylpolysiloxane with copolymeric terminal groups R such as:

in which R is a partially unsaturated hydrocarbon group of 20 from one to 20 carbon atoms or more, eg, octene, butene, ethyl phenylene, or tetradecene.

Another type may be a conventionally blocked polydimethyl siloxane with an alkyl olefinic pendant group such as:

CH3 EHa CH3 CH3 wherein R is an alkyl radical of from one to 20 carbon atoms or more. The copolymeric pendants account for the varnish adhesiveness of the silicone containing coatings.

A third type may be the so-called copolymers of dimethylpolysiloxane and a polyoxyalkylene ether such as:

35 No. 9 CH; CH3

Where 2 in number 1, 2, 3 and 4 equal 2-10 or more. No. 5 CH3 CH CH Where a; is equal to 2 to 20 or more as a copolymer.

N0. 6 CH:

(ROJnH Where a: is equal to 2 to 10 or more and n is 1 or more.

25 No.7 0H on; on

Where it is equal to 2 to 20 or more and n is 2 or more.

No. 10 CH CH3 (EH; (CH;)aSiOSiiO 10 51mm),

Ha H CH;0( sHtO)u( aH8) CH:

N0. 11 [0.11 0 cH,0H,o CH,CH,SiO-] Where a: is equal to 1.5 or more.

50 No.12 OHQCIIK C|1H1CH3 (CHa);i i0 SiO SIiO Si(CH3) s H i CH CHgO (CaHuOhKCgHtO)13(C3H0CH3 [CHJOCHjCHgOCHgCHjl (a cyclic tetramer) No. 14 CH:

(CHalzS lOi-{JSHCHDJ HgCHgO (CgH4O)iCH CH CH3 CH i(Ca o) dit ht i t hcHgflcH,l0(A10);

0H3 CH3 3 No. 16

CH CHa l B ucmnsio siomcmo 0,11.o omnoomcmsqosit(1mm. No. 17

CHgCII; CHgCH; -SiCH CHgO(CHgCHgO)in(CH )50CH CH; iO-

No.18 N0. 28 on, 011,, on,

1113 a nooo cu, ,s io sli Si(CII,) ..0oo1t SiCH CH;O(CH CILO)1n(CH,) OCH,CH -Si0 )113 43 X )Ha (II) N0. 2'.) (3001-1 snark); CIh-Si-CH; 4 CH3 CH (0H,)" on ClI;bli-O b i0 Si-O- SiClI s'uonm 3 x 0113 21H; x (311; .y' om 0H,0H,0 oH,oH,0)nGH, -Sli0- E CH1 0 (011201110) "CH1 l lnstead of curing a solution of resin and polysiloxane on the wire, the modified resin coatings of the invention may be No. 15 I pre ared b reacting, in a suitable vessel, the polysiloxanes CH'CHO(CaHGmMCHOCHE witl za resin by graft copolymerization. Suchia reaction can'be a accomplished by using a partially polymerized ester, such as (CHQJSKK i0)3 i0 an oil-free terephth'alic acid-type resin, and carboxyalkyl I O polysiloxane, such as carboxy ethyl methyl poly dlsiloxane. 2 Most reactable carboxy, hydroxy, or hydrogen terminated t )u( s alkyl aryl, or di alkyl polysiloxanes may be successfully used No.21 under proper processing conditions. The polyester resin is CH; CH3 heated to a proper esterification exchange temperature. The (cHmsi OSECHICHKO CIHODO CH reactable polysiloxane is then added with an ester interchange catalyst such as htharge or a metal acetate. These are the so CH: 5 CH3 called alcoholysis catalysts. Other examples of these catalysts OH; OH; are lead oxides, lead acetates, zinc oxides, cadmium acetates, (oHmsi OSFGHICHF)CHMOCHCH cuprous acetates, and zinc acetate. The carboxy and/or hydroxy groups present on the polysiloxane chain react with CH3 8 the -COOR groups of the ester to form free radicals for a H3 H3 linkage or react as a poly basic acid with excess hydroxyls, or (CHmsi OQJOECHICHAOQH) 100 both. This results in a copolyrner having a polyester backbone CH OH with pendant polysrloxanes dispersed along the chain. Solu a 8 3 3 tions of resins such as these may be used per se or incorporated with conventional coating resins as wire insulating coatings having the desired slip and other physical properties. GHAC HQ O(C;Ht0) OHrC They have improved solution compatibility as either an over- OH: CH3 CH3 CH3 CH1 coat enamel or as the sole enamel on the wire. v A third method of preparing coatings for satisfactory use in CHalcam)owsmohlcHicfiomso S10 this invention comprises introducing the polysiloxane in a CH; CH; 4 CH; 4 CH3 polymer backbone during the preparation of a conventional CH3 CH3 0 resin top coat. Such hybrid resins may be used asslippery top coats and/or as slippery base coats depending'upon the type.

I l l. CHM-Jam) T Such a material is a polyester polysiloxane wherein terephthalic or isophthalic acids or their half esters are reacted with 23 CH CH3 CH3 suitable polyols and an organosilicon in a conventional l manner. A portion of the polyols or the acid is substituted for organosilicon compounds containing reactable H, OH,

I I CH3 COOH. Examples of suitable organosilicons are diphenyl N0. 2 (3E1 (I333 silanediol, carboxy alkyl polysiloxanes, carboxy-terminated CH3-Si 0-si O-Si-CH alkyl aryl polysiloxane. Terephthalic acid, a glycol'and the sill E x (lJH3 icon compound are reacted together in suitable equipment to Where R is a higher molecular weight hydrocarbon side chain produce a resm' Resms of this type may be used alone or as Such as heptene, hexene' butene propane propylene additives to conventional wire topcoating resins to produce tetradecene, pentene, octene, or decene. coatmgs havmg low coefficlgnf of fncuon' Another means of combining the polysrloxanes with con ventional coating resins in accordance with this invention is by 25 CH3 CH3 emulsifying the polysiloxane in an oil/water emulsion. Several l magnet wire base coatings are applied from water, for example, acrylic and polyester resins. These base coats may be CH3 CH3 1 CH1 dispersions or emulsions. In order to gain a slippery surface, N0. 26 (3H1 (3H1 CH3 one or more coats of polysiloxane modified resin may be placed over the base coat applied from water. Better still, the 5 l l k polysiloxane of this invention (example 9) may be emulsified N0. 27 with the help of small quantities of surfactant and added to the I water base coat resin used. RO-S|i OSli -O-SiOR M CH= a. 2 3..

EXAMPLE 1 Wherein R and R of examples 25, 26, 27 may be the same or different radicals or organic hydrocarbons having one Copper wire having a base coating of lsonel 200E (Class H to 20 or more carbon atoms, or may be -OH, -H, or polyester wire enamel) was topcoated with the following com- COOl-Las the following: position:

ingredients Parts by Weight Nylon type 616 l6% solution in a solvent mixture of phenol, cresylic acid and E.W. naphtha) 98 Methyl Alkyl polysiloxam: 2 Iron Octoate (6%) 0.2

The nylon siloxane solution was applied in two layers over the base coat and each layer was cured in a wire tower at a temperature ranging from 275 at the bottom to 475 C. at the top. The coating after curing had a coefficient of friction of 0.095. Another example of the base-coated wire was topcoated in the same manner with the nylon solution, omitting the polysiloxane and the iron octoate. This wire had a coefficient of friction of 0. l 87.

Bobbins were wound at high speed on a winding machine with great case using this coated wire. In spite of the slipperiness of the surface, electrical adhesive tapes and electrical of 2,400 hours while the conventional nylon-coated wire tested 15.42 hours. v v

EXAMPLE2 Copper wire treated as indicated in example 1, the base coating of lsonel 200E being topcoated with the following composition:

Ingredients Parts by Weight Polyethylene terephthalate l3% solution in orthochlorophenol and orthocresol) 680 Methyl Butyl polysiloxane 15.6 Iron Octoate (6%) so This coating solution was applied as indicated in example 1, and the coefficient of friction was found to be 0.109. A second sample was prepared having a topcoating of the polyethylene terephthalate (Mylar) solution without the silicone or iron octoate. The coefficient of friction of this wire measured 0.183.

EXAMPLE 3 Copper wire having a four-layer base coating of lsonel 200E was topcoated with a resin having the following composition:

Ingredients Parts by Weight Polytrimellitamide-imide polymer 18%) solution in cyclohexancne and N-methyl pyrrolidone) I Methyl tctradecyl polysiloxane 0.8.

This solution was applied in two layers, each of which was cured in a wire tower as indicated in example 1. Another sample of the same base-coated wire was top coated in the same manner with the same composition except that the siloxane was omitted. The composition with the siloxane had a coefficient of friction of 0.127 while the one without had a coefficient of friction of 0.192. The polytrimellitamide-imide polymer is reactive with the free radical produced in the polysiloxane above 170 C. and upon curing produces a smooth, hard resin without the necessity of added catalyst.

Amoco Chemical Co. Al-IO resin or a condensation product of Trimellitic anhydride acid chloride and p,p'oxybis (aniline). See US. Pat. Nos. 3.347.828; 3,320,202 and 3.377.32l.

EXAMPLE 4 Copper wire having a base coat of a commercial Class F polyester magnet wire resin was top coated as described in example l, with the following composition:

Ingredients Farts by Weights Nylon 6/6 [6% solution in a solvent mixture of phenyl, cresylic acid and EM. naphtha) Phenyl ethyl polysiloxane Cobalt Octoate (6%) After curing, this topcoat composition had a coefficient of friction of 0.1 13. A second sample of the same wire was overcoated with the nylon solution from which the polysiloxane and catalyst were omitted. This wire had a coefficient of friction of0.l 77.

EXAMPLE 5 Copper wire having a base coating of siloxane alkyd modified terephthalic acid type polyester was overcoated with the following composition:

Ingredients Parts by Weight Nylon filo (lo'lb solution in a solvent mixture of phenol. cresylic acid and E.W. naphtha) Co-polymcr of dimcthylpolysiloxane and polyoxyalkylenc other Catalyst lOO EXAMPLE 6 Bare copper wire was coated with the following composition:

Ingredients Parts by Weight Nylon rv/n wk solution in a solvent mixture of phenol, crcsylic acid and E.W. naphtha) Carboxycthyl methyl siluxanc Catalyst This wire with multiple coats was cured as indicated in example l and the resulting coating had a coefficient of friction of 0.123. For improvement of other properties, a different base coat may be used with the nylon siloxane top coat.

EXAMPLE 7 Copper wire having a base coating of lsonel 200E (Class H polyester wire enamel) was overcoated with one coat of the following composition:

Ingredients Parts by Weight Commercial Class H polyester wire enamel Alkyl aryl siloxanc After curing, this topcoated composition had a coefficient of friction of 0. 103. A second sample of the same wire was overcoated with one coat of the above solution from which the polysiloxane was omitted and had a coefficient of friction of 0.177. The coating containing alkyl-aryl siloxane had improved burnout resistance compared to the conventional The resultant product was found to have a coefficient of friction of 0. l 30 while conventional polyesters not top coated had a coefficient of friction of 0.347.

overcoated lsonel 200E. EXAMPLE 1 1 EXAMPLE 8 Another resinwas prepared as in example 10 using the following composition: Ingredients Parts by Weight lngredients Parts by Weight Epoxy resin in solution) 310 10 Cobalt Octoate (6%) 2 Dimethyl terephthalate 460 Manganese Octoate (6%) 1 Ethylene l c l 210 Methyl epoxy alkyl siloxane 3.1 Trihydroxy ethyl isocyanurate 200 Trimethylol propane 130 Diphenyl silane diol 23 l 5 Zinc acetate 0.08 The above solution was applied in two coats as a topcoat over (Sumciem xylene msync acid a wire with four base coats of a commercial epoxy wire enamel for azeotropic disfillatiun) and cured in a wire tower as indicated in example 1. The wire with this composition had a coefficient of friction of 0.197. The same base coat was topcoated with the above epoxy resin 20 The above resin was dissolved in a blend of cresylic acid and without the siloxane and metal driers and had a coefiicient of aromatic hydrocarbons to 30 percent solids. Tetrakis (2-ethy1 friction of 0.330. hexyl) titanate was added as a coreactant catalyst as 2 percent of the solution. A bare copper wire was coated as in example 1 EXAMPLE9 using the above solution. The resultant end product had a lngrediems Pans by wcigm 25 coefficient of frictionof 0.147 while a conventional polyester had a coefficient of friction of 0.347.

Acrylic resin (24% emulsion in water) 90 EXAMPLE 12 Alkyl-aryl siloxane (40% emulsion y in water containing a nonionic wetting lngmd'cms Pans by agent) 1 agent) Cobalt OM03? (6%) 04 Conventional polyurethane wirc 98 Methyoctyl pnlysiloxanc 2 A wire coated with the above composition by conventional methods was found to have a coefficient of friction of 0.15 whereas the same composition without polysiloxane had a wlre coated the above compqsltlon l fom/emlonal ffi i f f i ti f0 19 methods was found to have a coefficient of friction of 0.097

while another wire coated with the resin having no polysilox- EXAMPLE 10 ane had a coefficient of friction of 0. l 8 40 Although in the above examples the wire was coated from g g g sg gg gg z iigs z i ggg z s gg222 13123: solutions of the modified resins, it will be appreciated that the E the re aration of the I Star resin The folloglin in solid resins may be applied to the wire by extrusion without i p P p0 ye detracting from the desirable properties achieved by the ingredients were placed in a four-necked reaction vessel with Vemion stirrer, thermometer, inert gas bleed, and a heated condenser: what I claim is:

1. An insulated electrical conductor having a baked-on lngmd'ems Pamhy resinous coating consisting essentially of the elevated temperature reaction product of a polytrimellitamide-imide film gzgfi f zgr 21 forming resin and from 0.01 to 25 percent by weight of a two Trimethylol propane 23 dimensional linear organo polysiloxane having the formula Carboxyelhyl methyl polysiloxane 2.3 Zinc Acetate 0.08 (Sufficient xylene or cresylic acid (3H3 CH3 l'or azeotropic distillation) OH3 o I Ha CH:

The reaction products were heated to 130 C. in 30 minutes. The zinc acetate catalyst was added and the temperature wherem R an alkyl group havmg from C atoms raised to 240 C. and held for 3 hours. The temperature was and then raised to 250 C. with viscosity determination used to in- 5 coatmg chractenld by a low coefficlem of dicate termination of the reaction. This period was approxicoupled wnh vamsh f mately 16 hour The reaction was then stopped and the resin 2. The conductor of cla|m l in which said polysiloxane 1S quenched with cresylic acid. The resin was then diluted to 30 a tePradecyl w i d percent solids with a 1 to 1 blend of cresylic orthocresol acid he Insulated e acme? con of clam l m wh'ch h and aromatic hydrocarbons and applied to wire in multiple g g i g havfng a coat of Polyester resm layers as a base coat. The wire was cured after each pass eneat Sal ba 6 resmous coatmg' through the solution at a temperature from 270 to 450 C. 

2. The conductor of claim 1 in which said polysiloxane is methyl tetRadecyl polysiloxane.
 3. The insulated electrical conductor of claim 1 in which the conductor is copper having a base coat of polyester resin beneath said baked-on resinous coating. 